An edge seal is commonly used as a mechanical barrier to contaminants introduced in the die sawing process, including moisture that may disrupt the performance of the integrated circuit device. A conventional edge seal consists of a combination of metal lines connected by line-type vias. Such an edge seal does not protect the chip corners from delaminating and cracking. During singulation, cracks sometimes develop, then propagate through the seal ring during reliability testing. Delaminations have been found to occur near corners where stress is highest.
FIG. 1 illustrates a top view of a conventional seal ring structure. Seal ring 11 encloses die 60. As shown in FIG. 2, seal ring 21 has a sloped corner area instead of a sharp corner to decrease stress. FIG. 3 shows a seal ring 31 having slots 33 within it. The slots may or may not help to decrease stress. FIG. 4 shows a repeated redundant crack stop seal ring 41. This seal ring has the disadvantage of taking up a lot of design space, not only at the corners, but along the whole length of the seal ring. It is desired to find a method of forming an edge seal that will not delaminate or crack.
Co-pending U.S. patent application Ser. No. 09/989,837 filed on Nov. 20, 2001 and assigned to the same assignees as the present invention describes a seal ring having alternating widths along its length. U.S. Pat. No. 6,300,223 to Chang et al and U.S. Pat. No. 5,831,330 to Chang teach the use of plugs in a seal ring to prevent cracking. U.S. Pat. No. 5,834,829 to Dinkel et al describes the redundant seal ring structure of FIG. 4. U.S. Pat. No. 6,028,347 to Sauber et al show trenches formed outside the seal ring at the corners. U.S. Patent Application 2001/0030358 to Okada et al teach a method of seam welding of the seal ring at the corners to prevent cracking.